Electrosensitive recording blank



June 7, 1966 H. R. DAL'roN 3,255,039

ELECTROSENS ITIVE RECORDING BLANK Filed May 28, 1962 Sou/ce of /7 T a Pedara/Mg j ,Vani-CoA/Duc r11/E PAPE@ INVENTOR. /fwm D R. ,D0/ TON BY Ma/6^ ATTORNEY United States Patent O York Filed May 28, 1962. Ser. No. 198,327 Claims. (Cl. 117-215) This invention relates to recording blanks and more particularly it relates to blanks of the electrically inscr1bable kind.

A principal object of the invention is to improve the surface characteristics and recording properties of electrically inscri-hable blanks by providing the blank with at least one novel aerated coating.

One kind of electrically inscribable blank which has yfound-wide acceptance in 'theA recording arts, :for example in the facsimile recording art, comprises a `backing sheet carrying a surface coating which coating is designed to Ibe disintegrated or eXplosively removed in response to electric potentials applied thereto by an electrically energized needle-pointed stylus. Examples of such blanks are those shown in US. Patents No. 2,483,220, No. 2,551,321, No. 2,664,043, No. 2,664,044, No. 2,951,019 and No. 2,951,441.

In general, the above noted blanks comprise a paper base or backing which may be conductive in itself, for example by having a conductive material in the body thereof, such as powdered carbon, or the backing may be of non-conductive paper having one of its faces coated with .la conductive film or layer. Usually the conductivity -of either type of backing is derived from the presence of conductive powdered carbon which imparts a dark or even black color to the backing or its coating. Over the dark conductive surface of the blank is then applied a top or masking coating which is usually light colored or even white, so that when the masking coating i-s removed or disintegrated in localized areas, it exposes the underlying dark surface and produces the desired readability contrast.

Heretofore, in order to provide the blank with a top it was found 4neces-sary to compromise with the hardness of the masking coating. Such hardness is usually obtained by using a resin binder for the White or light colored pigment in the masking coating. Therefore, it was considered necessary to limit the amount of binder so that the finished coating would have the desired sensitivity and accuracy of recording. The result is that While such a blank is well suited to produce electrically inscribable records thereon, the `surface is subject to surface marring during handling, storage, filing, etc. If sufiicient binder is used in the top or masking coating to increase the hardness thereof, it is found that the recording qualities are correspondingly degraded.

Accordingly, another principa-l object is to provide a top or masking coating for electrosensitive recording blanks, which coating has optimum hardness consistent with optimum recording and readability properties. As an ancillary result -the improved coating provides a good surface for wri-ting thereon manually with pen or pencil and for making erasure corrections when necessary and w-ithout rendering the coating easily removable by mechanical scratching.

Patented June 7, 19663 Ice Since the electrical recording on s uch blanks is essentially caused by an electrical breakdown, disruption or disintegration of the top coating, it is desirable that the breakdown in elemental orsignal-controlled localized are-as be effected at relatively low potential, for example of the order of volts. Since air has a lower breakdown potential than any of the resins, pigments or fillers that are usually incorporated in the filling, it has been found desirable to have as mu-ch air as possible in the form of microscopic bubbles, pockets or channels uniformly dispersed throughout the coating, but without disrupting-or fr'acturing the visible surface masking continuity of the film coating. While it might seem that the breakdown could be improved by greatly increasing the conductive :content of the coating using electrically conductive resins, pigments or fillers, such a contemplated solution, if not controlled with utmost precision, while it may 'lower the breakdown potential, nevertheless `dissipates the energy of the recording current over too large a localized area beneath the point of the recording stylus. In other words, it tends to degrade the fineness of resolution in the recordings. This, of course, is particularly true where the signals are applied to the blank by a needlepointed electrically energized stylus, a desideratum being to confine the disruptive energy to the minute or elemental area directly beneath the point lof the stylus. According to the present invention, this fineness of resolution is achieved by physio-chemically introducing a multiplicity of microscopic air pockets or channels distributed throughout the top coating.

A feature of the invention relates to Ia signal disruptable coating for electrosensitive blanks, which coating has substantially uniformly distributed throughout its physical structure a multiplicity of microscopic pockets or channels which are physio-chemically `formed within the coating.

Another feature relates to an improved coating batch lfor mak-ing the top or masking coating of an electrically inscri-hable blank, which batch includes a light colored comminuted pigment, one or more resin binders and a -com-minuted solid chemical compound which, when heated, produces a multiplicity of gas pockets or channels within the batch when the latter is dried to form a continuous film.

A further feature relates to the novel organization land compositions which constitute an improved top or masking coating for electrosensitive recording blanks.

Other features .and advantages, not specifically enumera-ted, will `be apparent after a consideration of the following -det-aled descriptions and the appended claims.

In the drawing,

FIG. 1 `shows the invention embodied in one known kind of recording blank;

FIG. 2 shows the invention embodied iin another known kind of recording blank;

FIG. 3 shows the invention embodied in a blank of the stencil-forming kind;

FIG. 4 is a highly magnified sectional view taken along the line 4-4 of FIG. 1; A

FIG. 5 is an even more highly magnified sectional view taken along line 5 5 thereof;

FIGS. 6, 7 and 8 are views of modified blanks embodying the invention.

Referring to F'IG. l, the numeral 10 designates an electrosensitive recording blank comprising an electrically ,conductive backing ,11,1 which may be of paper, card;

board, fiber, metal foil, and the like, which in itself is a conductor. Thus, if the backing 11 is paper, it may have incorporated therein a conductive material such as powdered conductive carbon, powdered metal, and the like. This causes the backing to have a black or dark colored appearance. Adhesively coated on to the upper surface of backing 11 is athin masking .coating 12 which usually includes `a white or light colored comminuted pigment, such as powdered zinc sulfide, zinc oxide, titanium oxide, or a mixture thereof. Thepig'ment may include Ia phosphor activator, such as is generally used in the manufacture of luminescent coatings. The coating 12 also includes a nlm-forming binder, such as .a resin, a gassing agent as hereinbelow described, and if desired a .coloring material such as a colored' pigment or the like. I-t will be understood, of course, that the coating 12 is prepared as a liquid or viscous batch rand is then applied to the sheet 11 so that, when dried thereon, it forms a film of the desired thinness.- yIn general, this lm should be as thin as possible consistent with the desired masking properties that are to be obtained, since the formulations for coating 12, without the said gassing agent, are well-known in .the art, detailed description thereof is not necessary herein but reference may behad for that purpose to any of the above noted United States Letters Patent. A typical formulation containing the said gassing agent is given hereinbelow. f

Instead of employing a backing which is .conductive by reason of conductive material in the body thereof, the backing, as shown in FIG. 2, may be of non-conductive material having a conductive coating 13 thereon. FIG. 2 the blank is supported on `a conductive platen or drum, shown in dotted lines, which may be grounded.

v1n accordance with the present invention, the liquid batch which is used to form the coating 12 also includes one or more iinely divided comminuted chemical compounds which have the property of releasing microscopic gas bubbles when heated to the temperat-ure required to dry t-he batch on the backing 11, which temperature is usually between 220 degrees F. and 500 degrees F. The following are some of the gas bubble-forming or channel-forming compounds that may be used:

4,4 -Oxybis (benzenesulfonyl semicarbazide) 4,4 Oxybis (benzenesulfonyl hydrazide) azodicarbonamide N,N' dimethyl N,N dinitrosoterephthalamide Trihydrazino-sym-trizine Barium azodicarboxylate Bis-benezenesulfonyl hydrazide It will be understood that the invention is not limited to lthe above compounds, one of the requisites being that the compound decompose at a temperature within the working range of the b'lank drying equipment so as to release a multiplicity of microscopic gas bubbles. vIt is also desirable that such compounds be non-toxic and nonhazardous in use. Furthermore, since the masking coating should preserve its wvhite or light colored character, it is essential that, when the coating is completely dry, the bubble-forming portion does not change the iinal color of the masking coating. Likewise it is important that the drying time and temperature be regulated .with respect to the viscosity of the coating batch so that `the gas bubbles do not result `in permanent breaking or tfracturin'g of the finished coating. It has been found that by using a resin binder of the thermoplastic kind, as distinguished from a binder of the thermosetting kind, the solid particles of the chemical compound can be directly disintegrated by heat without danger of fracturing the finished iilm. It has also been found `that when using azodicarbonamide as the bubble-forming compound in the batch a slightly yellow coloration is produced before drying, but after drying of the batch and the decomposition of the compound has been completed the finished coating loses its yellowish coloration and returns to .the desired white or f5.- light `colored character. This change in coloration during the drying operation can be used .as an indication that the desired decomposition and bubble-forming have been completed.

If desired, the coating batch may also include any of the well known plasticizers, such as dioctyl phthalate, dioctyl ladipate, dioctyl sebacate, tricresyl phosphate, dioctyl hexahydro phthalate, cresyl diphenyl phosphate, polyesters, etc., or any of lthe well known stabilizers, such as di-basic lead phthalate, di-basic lead phosphite, bariumcadmium-zinc types, calcium ethyl aceto acetate acetate, etc.

I have found that the addition of certain stabilizers tend to lreduce the time required to complete the decomposition of the bubble-forming agent. Thus, in the case of a batch incorporating a thermoplastic resin binder, zinc oxide pigment, a bubble-forming agent of azodicarbonamide, and lead phthalate stabilizer, the desired bubble formation is effected in approximately one-half the time required when such formulation does not contain the lead phthalate stabilizer. Certain pigments, chlorinated compounds, etc., |have similar effects.

Furthermore, by adding one of the above mentioned solid gassing agents to a top coating of the formulations described, for example in any of the above noted patents, the percentage of thermoplastic resin binder may be increased from 5 percent to 30 percent with the gassing Iagent constituting from 0.5 percent to 8 percent of the dry weight of the resin binder. This coating, when applied for example to an electrically conducting paper such as disclosed in U.S. 'Patent 2,328,198 and dried thereon at a temperature above the decomposition temperature of the solid gassing agent, produces an electrosensitive blank which has a harder top surface without deterioration in the precision and sharpness of the -recordings thereon.

It is not possible to state precisely the way the aerating agent functions in the coatings disclosed. .'It seems that when the decomposition temperature is attained the gas produced is broken up into microscopic bubbles by the pigment particles. Some are trapped land some reach the surface by channeling their tway through the coating, as illustrated in the highly magnified view of FIG. 5. in any event the effect upon the recording is the same since microscopic cavities result from the decomposition. The gassing agents in general leave very little residue 'after decomposition. This residue is so small that it has not been 4observed microscopically and does not have any effect upon the recording properties of the blank.

The following is a typical example of a preferred yformulation for the manufacture of a yblank of the kind illustrated in FIG. 1 wherein the backing is of conductive paper:

Example 1 This example utilizes azodicarbonamide mechanically dispersed in a coating.

Parts by weight VResinpolyvinyl butyral (intrinsic `viscosity of approximately 1.2) 8.0 Solvent-methanol 120.0 Stabilzer-tricesyl phosphate 1.0 Plasticizer-di-basic lead phthalate 0.2 Pigment-zinc sulfide 44.0 Gassing agent-azodicarbonamide 0.15

The above ingredients, with the exception of the azodicarbonamide, are placed in a ball mill -an-d ground for approximately twenty-'four to thirty hours. At the end of this time the zinc sulfide shall have kbeen thoroughly If a blank of the type shown in FIG. 2, employing a non-conductive paper 11a having a conductive coating 13, is to be produced, care must be exercised in the choice of the resin used in the conductive coating 13 in order to prevent that coating intermingling with the masking coating 12 at the drying temperature of the latter. A typical example of a preferred formulation for the conductive coating 13 is `as follows:

Example 2 Y Parts vby Weight Methyl cellulose (400 cps.) 6.0

Gas black (Dixie No. 5 manufactured by United Carbon Co., Inc.) 20.0

Water 200.0

As above pointed out, the invention is also applicable to blanks of the stencil-forming kind, such as disclosed for example in U.S. Patent No. 2,664,043 and illustrated in FIG. 3 of the drawing, consisting of non-conductive paper or cardboard backing 14 to which is adhesively but strippable attached a conductive plastic film 15 carrying a masking coating 12 of any of the above formulations. Here again, care must be exercised in the choice of the resin used in making the film 15 so that it does not intermingle with the coating "12 at the drying temperature of the latter. When the Iblank of FIG. 1, for example, is recorded on by a needle-pointed stylus 16 energized from any well known source of recording voltages 17, it results in a disintegration of the coating y12 only in minute perforation 18 through which is revealed the black color of the backing 11. As indicated in FIG. 4, the coating 12 contains the lmultiplicity of microscopic air bubbles resulting from the heat decomposition of the gassing agent in the coating 12. On the other hand, when the blank of FIG. 2 is recorded on, since the backing 11a is a conductor, the masking coating 12 is removed to reveal the black surface of the coating 13. In the Iblank of FIG. 3, since the backing 14 likewise is a non-conductor, the recording currents perforate both the masking coating 12 and the plastic film 15 which can be stripped bodily as a unitary sheet from the backing 14 to form a duplicating stencil.

It will be understood, of course, that the showing of FIG. 4 with respect to the size and distribution of the -aerated or gas pockets 17 is essentially diagrammatic,

and the pocket `size is much less than as shown and the number of the individual pockets is much greater than as shown. Preferably the size of the individual gas pockets should not be of the same order as the size of the recorded perforations, for example recorded perforation 18 in the coating 12. Furthermore, while FIG. 4 shows the pockets in the form of discrete bubbles, it may very Well -be that during the decomposition some of these bubbles coalesce or line up to produce a channel or channels 19 in the coating 12. However, the width "w of these channels is of a much lower order than the width of the recorded perforations 18, as represented in the even higher magnified view of FIG. 5. In any event the bubbles or channels resulting from the heat decomposition are of such microscopic size as not to be visible to the naked eye and do not detract from the masking effect of the coating 12.

The invention is not necessarily limited to the particular form of blanks hereinabove described Ibut is applicable to Ia wide variety of blanks having a top coating which is to be removed or disintegrated in localized areas in response to applied electric voltages. Thus, in the embodiment of FIG. 6 the blank may consist of a non-conductive paper 20, the non-recording side of which is provided with -a film or plate 21 of metal such for example as aluminum foil. The recording side of this paper may have the black conductive coating 13 on which is superposed the aerated masking coating 12 above described. FIG. 7 shows another form of blank embodying the invention, comprising for example a non-conductive paper 20 'having its recording side provided with a conductive metal film or plating 22 on which is superposed the aerated masking coating 12 above described. 4In the event that the backing 11 (FIG. l) is of conducting paper, it may, if desired, have a metal backing, such for example as aluminum, applied to its bottom surface, as indicated in FIG. 8.

The expression electrically conducting backing, as employed herein, means a backing which is electrically cond-uctive by reason of the incorporation of conductive material in the body thereof, or by one or more conductive coatings applied thereto.

What is claimed is: i

1. An electrosensitive recording blank of the kind having a conductive substrate, and having an aerated top surface coating which is removable in localized areas when electric disrupting voltage is applied thereto, said coating including a masking pigment, a film-forming binder and a multiplicity of discrete microscopic gas pockets substantially uniformly dispersed throughout the coating.

2. An electrosensitive recording blank according to claim 1 in which said pockets are of microscopic size resulting from the heat decomposition of solid particles while within the coating material.

3. An electrosensitive recording blank according to claim 1 in which the binder is a thermoplastic resin and said coating is in the form of a continuous film free from fracture lines.

4. A n electrosensitive recording blank having an electrically conductive dark-colored backing, and a lightcolored masking coating comprising an aerated film wherein the aeration is constituted of a multiplicity of microscopic air pockets formed by heat decomposition of solid particles while in said film.

5. An electrosensitive recording blank, comprising a dark-colored conductive backing havin-g a light-colored top masking coating, said masking coating comprising a light-colored masking pigment in a thermoplastic filmforming binder, and a multiplicity of substantially uniformly dispersed microscopic air pockets resulting from the heat decomposition in situ of comminuted solid particles within the coating.

6. An electrosensitive recording' blank according to claim 5 in which the said particles prior to decomposition constitute from 0.5 percent to 8 percent of the dry weight of the resin binder.

7. The method of making an electrosensitive blank of the kind having a coating which is removable in localized areas when disruptin-g electric voltage is applied thereto, which comprises -preparing a viscous coating batch comprised of a masking pigment, a film-forming binder and a comminuted solid gassing compound, applying the batch in a vicous condition as a coating to a backing, and then drying the coating of said backing at a temperature above the decomposition temperature of said compound to convert the coating to a dry continuous film having a multiplicity of discrete microscopic air pockets dispersed uniformly dispersed gas bubbles in said maskin-g coating,

the binder in said masking coating being different from the binder in the conductive coating to prevent the two coatings intermingling when said agent is raised to its decomposition temperature.

7 10. An electrosensitive blank according to 4claim 9 in 2,358,839 which said conductive coating includes powdered carbon 2,664,043 and a. resin binder. 2,739,909 2,837,440 References Cited by the Examiner 5 UNITED STATES PATENTS RICHARD D. NEVIUS, Primary Examiner.

WILLIAM D. MARTIN, Examiner.

A. H. ROSENSTEIN, Assistant Examiner. 

4. AN ELECTROSENSITIVE RECORDING BLANK HAVING AN ELECTRICALLY CONDUCTIVE DARK-COLORED BACKING, AND A LIGHTCOLORED MASKING COATING COMPRISING AN AERATED FILM WHEREIN THE AERATION IS CONSTITUTED OF A MULTIPLICITY OF MICROSCOPIC AIR POCKETS FORMED BY HEAT DECOMPOSITION OF SOLID PARTICLES WHILE IN SAID FILM. 